CN1342269A - Apodization of optical filters formed in photosensitive media - Google Patents
Apodization of optical filters formed in photosensitive media Download PDFInfo
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- CN1342269A CN1342269A CN99810053A CN99810053A CN1342269A CN 1342269 A CN1342269 A CN 1342269A CN 99810053 A CN99810053 A CN 99810053A CN 99810053 A CN99810053 A CN 99810053A CN 1342269 A CN1342269 A CN 1342269A
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
- G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
- G02B6/02123—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating
- G02B6/02133—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating using beam interference
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/58—Optics for apodization or superresolution; Optical synthetic aperture systems
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
- G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
- G02B6/0208—Refractive index modulation gratings, e.g. Bragg gratings characterised by their structure, wavelength response
- G02B6/02085—Refractive index modulation gratings, e.g. Bragg gratings characterised by their structure, wavelength response characterised by the grating profile, e.g. chirped, apodised, tilted, helical
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
- G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
- G02B6/02123—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating
- G02B6/02133—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating using beam interference
- G02B6/02138—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating using beam interference based on illuminating a phase mask
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29346—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by wave or beam interference
- G02B6/29347—Loop interferometers, e.g. Sagnac, loop mirror
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- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Optical Integrated Circuits (AREA)
- Diffracting Gratings Or Hologram Optical Elements (AREA)
Abstract
Filter gratings are formed in optical waveguides (50) having photosensitive cores by exposing the cores to actinic radiation in the form of interfering beams (38, 40) having peak intensities (72, 74) that are relatively displaced along an optical axis (64) of the waveguides. Each of the interfering beams has a single-lobed intensity profile and a degree of spatial coherence required to achieve a desired fringe contrast between the two relatively displaced beams. Index modulations in the photosensitive core match the illumination (interference) pattern of the radiation. The relative displacement of the interfering beams reduces side lobes of the gratings' spectral responses by leveling the average refractive index of the index modulations. A second exposure with the two beams but without the beams' interference effects further levels the average refractive index.
Description
Technical field
Exposure (for example, interfering) by form pattern under actinic radiation can form light filter in photosensitive optical medium, this kind light filter generally has the logical or band resistance spectral response distribution curve of band.Competitiveness to variations in refractive index in the medium requires to have increased undesirable " structure " (for example, secondary lobe) to the Response Distribution curve, and these " structures " can be handled by the various toe technology of cutting.
Background
Bragg grating and long-period gratings are the examples of the light filter that forms in photosensitive medium by form the exposure of pattern under actinic radiation.The fibre core of these light filters generally is mixed with germanium and so on photosensitive medium, and this photosensitive medium can make fibre core change its refractive index in response to the actinic radiation exposure, and actinic radiation is generally in the ultraviolet spectral limit here.Illumination radiation generally can raise and be exposed the refractive index of part in the fibre core, and the rising of refractive index is proportional to radiation intensity and exposure length (time).
Can form required pattern by interfering or sheltering, and will control stiffness of coupling and grating cycle in the pattern forming process.The cycle of Bragg grating, this grating preferably interfered the two-beam radiation laser beam to be realized by the oblique angle less than half of the centre wavelength of spectral response.The macrocyclic cycle is 100 or 1000 times, can inscribe by simple masking method.For example, can form pattern, make the light belt irradiation fibre core of apart, thereby form long-period gratings amplitude mask.
Regardless of Exposure mode, the intensity distributions of illumination radiation all can change into the index distribution of analogous shape in the fibre core.For example, the illumination beam with constant intensity distribution can produce uniform index modulation and constant mean refractive index along the exposed portion of fibre core through interfering or sheltering.But there is bigger secondary lobe in resulting spectral response in ideal band resistance both sides.Illumination beam with more typical gaussian shape, the index modulation of its generation and mean refractive index are also followed gaussian shape.The gauss change of index modulation value helps to eliminate the both sides secondary lobe, but the variation of the mean refractive index of being followed can make gradually change the effective period of grating, and generally can produce secondary lobe in a side of ideal band resistance.
Be sometimes referred to as " cutting toe " for eliminating the raster correction that undesirable secondary lobe does, because it has comprised the operation that the grating amplitude " is covered ".The purpose of cutting toe generally is in order to make the index modulation value obtain the variation (for example, gaussian shape perhaps more generally, increases to the shape that peak value reduces then earlier) of pulse type, to keep constant effective period on the overall optical gate length simultaneously.Many known technology costlinesses, consuming time that are used for grating is cut toe perhaps are difficult to the precision that reaches required.
For example, the United States Patent (USP) 5,367,588 of authorizing people such as Hill is close to a nonlinear phase mask and is fixed on the photosensitive light filter medium, in order to the interference figure of a non-uniform spacing that medium is exposed.This phase mask itself plays the grating effect, and it is divided into the interfering beam that two bundles can form non-homogeneous interference figure with a branch of beam of actinic radiation with gaussian intensity profile.The varied pitch of gained light filter grating has compensated the distribute variation of corresponding mean refractive index of combined strength with illumination beam.The manufacturing expense of this special nonlinear phase mask is very high, and has increased the production cost of light filter greatly.
The United States Patent (USP) 5,717,799 of authorizing Robinson also advises proofreading and correct and being accompanied by the desirable variation that change, undesirable mean refractive index of index modulation value by changing the grating cycle.Individually inscribe each raster unit for realizing that suggestion that this target proposes comprises, perhaps during preparation (exposure) raster unit, strain the various piece of grating discriminatively.For typical Bragg grating, its cycle has only half micron such little, so it is less feasible to inscribe indivedual raster units, and strains the complicacy that the grating various piece can increase manufacturing greatly discriminatively, and causes the inconsistent result of possibility.
Authorize people's such as Mizrahi United States Patent (USP) 5,309,260 and Bragg grating is cut toe by continuous exposure.Exposure for the first time is to restraint the interfering beam with Gaussian distribution with two to produce required variation in index modulation.Exposure is the mean refractive index of rising grating one end for the second time, thereby suppresses the sub-peak (fine structure) of filter spectra response.But still there is variation in homogeneous refractive index along grating length, and its effect is similar to " chirp ", and it can produce undesirable time dispersive (temporaldispersion) in optical filtering signals.
Brief summary of the invention
Our invention is that the variation with the index modulation value separates along the small part that is changed to of light filter optical axis with mean refractive index, thus to the response curve shaping of light filter.The most handy a branch of beam of actinic radiation with single-lobe shape intensity distributions of index modulation is exposed and is formed.Can further influence mean refractive index with identical or different exposures along optical axis.
An example is to merge the two-beam radiation laser beam, forms the interference figure with suitable cycle on the photosensitive fibre core of specifying light filter.Two-beam from a branch of public, have a sinc
2The space coherent beam that proper strength distributes.The axle of two light beams mutually tilts, and in order to regulating the fringe spacing of interference figure, and the axle of two light beams preferably is positioned on the coaxial plane of light filter, makes the optical axis of the transversal light filter of stripe direction.But the intersection point of two axles departs from optical axis, causes diaxon to produce relative displacement along optical axis.For having sinc
2The interfering beam of intensity distributions, axial spacing are preferably about 0.88 FWHM (full duration at half maximal value amplitude place).
In general, any departing from all can be reduced fringe contrast greatly, because interfering beam spatially departs from each other at the place, point of crossing of itself and light filter optical axis.Then, the most handy a kind of spatial light filter increases the spatial coherence of gained interfering beam, thereby allows its desired dislocation public beam shaping.Some is short for resulting interference figure, but has kept the contrast distribution and the identical fringe spacing of pulse type.Suffered the having the greatest impact of merging intensity distributions of two-beam.
Interfering beam has reduced the axial variation of light beam merging intensity in its overlapping region along the offset peak intensity of light filter optical axis.Influence to light filter is, more constant mean refractive index is provided in the overlapping region, makes the index modulation value keep the variation of desirable pulse type simultaneously in the same area.Fringe contrast is the basis of index modulation, and it reduces towards the two ends of overlapping region, because the intensity between the two-beam there are differences.Novel light filter has smooth spectral response, and sidelobe structure is dwindled.
Another example of the present invention is, spatial light filter is combined with the biasing phase mask, produces similar spectral response.Spatial light filter has increased the spatial coherence of beam of actinic radiation, and the best vertical incidence phase mask of beam of actinic radiation.Phase mask becomes the first order of opposite in sign with most of radiation diffractions, and disperses from phase mask and to become interfering beam.
But, do not resemble usually done phase mask be placed directly in inscribe grating on the light filter medium, but with phase mask and light filter medium from a distance, the peak strength that causes interfering beam is separated along the optical axis of light filter medium.The adjusting of fractional dose is similar to previous embodiment, makes the merging intensity of interfering beam along constant relatively in the overlapping scope of the light beam of optical axis.Same and previous embodiment is similar, and the index modulation that is formed by the gained interference figure numerically keeps pulse type to change.
The exposure for the second time and the first time can be exposed combines, and further improves the spectral response of light filter.Once more, on the position that separates along the light filter optical axis, use two-beam simultaneously.But, the beam spacing difference of double exposure.Exposure for the first time forms desirable index modulation, and exposure is for the second time cooperated with exposure for the first time, makes mean refractive index smooth.Two-beam comprises the source that is used for interfering beam when exposing for the first time from same source.But exposure does not for the second time rewrite index modulation in the light filter medium.In exposure for the second time, replace spatial light filter with amplitude mask, so that to the further shaping of overlapping light beam, but spatial coherence is lowered to the degree that is enough to prevent to form striped.Another kind method is that dither light filter medium or phase mask are so that on average form the exposure intensity (that is, " washing out " striped) of the irradiation of pattern.
The most handy interferometer of index modulation or the phase mask of Bragg grating are inscribed, and are preferably in the similar device of use when exposing for the second time.Double exposure can be accumulated, so their order can be put upside down.The index modulation of long-period gratings can be inscribed with the lower instrument of sensitivity.For example can inscribe grating with amplitude mask with rectangular transmission function.But the most handy phase mask that can produce the relative divergent beams of two bundles replaces amplitude mask, regulates mean refractive index with the two ends at grating, washes out striped simultaneously.
Accompanying drawing
Fig. 1 is a curve map, shows refractive index along the photic variation of grating as function of position, wherein grating be through two bundles between the complete overlapping light beam the interference figure exposure and form.
Fig. 2 is a curve map, and it is used as the expectation spectral response that the reflectivity of function of wavelength comes grating in the presentation graphs 1.
Fig. 3 is the figure of an interferometer, and this interferometer is through arranging to make that being positioned at the locational two-beam of space displacement along the waveguide optical axis interferes.
Fig. 4 is a curve map, illustration the index modulation that is produced through two bundle space displacement light beams exposures.
Fig. 5 is a curve map, shows the spectral response relevant with index modulation among Fig. 4.
Fig. 6 shows the optical arrangement that produces two bundle space displacement light beams with phase mask, and wherein phase mask departs from irradiated waveguide.
Fig. 7 is a curve map, illustration by increasing exposure for the second time but do not produce the index modulation that further interference effect forms between the two-beam.
Fig. 8 is a curve map, shows the spectral response relevant with index modulation among Fig. 7.
Describe in detail
Top two accompanying drawings, Fig. 1 and Fig. 2 have drawn and have expected to have the result that the interfering beam exposure of gaussian intensity profile obtains by the photosensitive fibre core of optical waveguide through two bundles in the past.Two-beam produces an interference figure, and the fringe contrast of interference figure changes along photosensitive fibre core as the function that light beam merges the back gaussian intensity profile.In this example, fiber core refractive index is as the function of exposure intensity and increase, and changes according to the fringe contrast of interference figure.Therefore, the index modulation 10 of gained numerically changes along fibre core according to the gaussian intensity profile of combined light beam.
For clarity sake, only show several index modulation 10.(for the Bragg grating that is operated near the infrared wave strong point 1550nm, the gap periods of its index modulation 10 generally is approximately half micron.) modulation 10 peak valley numerical value change along photosensitive fibre core begin to reduce gradually from the center as desired to both sides, but the associated change by the mean refractive index of line 12 expression exists undesirable, as to change effective grating cycle structure, promptly changes the light path in cycle.Additional wavelength beyond the desired wavelength bands can satisfy conditioned reflex, and the grating that obtains thus can present chirp, and this pulse meeting makes optical filtering signals produce undesirable time dispersive.
Fig. 2 has drawn the expectation spectral response of the grating with refractive index pattern shown in Figure 1.The spectral response of gained comprises many secondary lobes 14, and these secondary lobes have comprised 16 more short wavelength's the reflections in addition of ideally-reflecting band, claims these reflections to have increased undesirable " structure " for the Response Distribution curve sometimes.
The present invention provides an additional degrees of freedom in its one or more embodiment, be used to make mean refractive index 12 smooth, keeps the peak valley numerical value of index modulation 10 to be the pulse type variation simultaneously.Fig. 3 and Fig. 6 show two such embodiment.
The embodiment of Fig. 3 is arranged to an interferometer 20, and it has lasing light emitter 22, is used to produce a branch of photochemical, temporally coherent radiation light beam 24.Lasing light emitter 22 can be the frequency multiplication dye laser of quasi-molecule pumping, and operating wavelength range is used to inscribe grating between 200nm and 250nm.Yet, also can use other laser instrument and other wavelength in conjunction with material to other wavelength and power rating sensitivity.Can use pulsating wave or continuous-wave radiation.
Cylindrical lens 26 convergent beams 24 make it pass through focal line 28.Be arranged in the spatial high-frequency component that near focal line 28 spatial light filters 30 shift light beams 24, to improve the spatial coherence of light beam.U.S. Provisional Application 60/047,859 has disclosed the details of the spatial light filter 30 of our first-selections, and the name of this application is called " spatial light filter that is used for high-power laser beam ", and its content is included in this by reference.After leaving spatial light filter 30, light beam 24 has sinc
2Intensity distributions.Collimating apparatus 32 is with light beam 24 collimations, and second spatial light filter 34 is from its sinc then
2Remove secondary lobe in the strength distribution curve.
Cylindrical lens 60 and 62 orientation are perpendicular to cylindrical lens 26, and their assemble the focal line in the coaxial plane (that is the figure plane of Fig. 3) of light beam 38 and 40 each comfortable waveguide 50 towards it.The width of each light beam is about the 5-100 micron, so light beam is along the length of optical axis 64 overlapping about 5-30 millimeters of waveguide 50.The energy density of illumination radiation estimates to be approximately 200mJ/cm
2/ pulse
Waveguide 50 can be adopted such as forms such as optical fiber or plane eyeglasses.Waveguide 50 has an exposed part 66, and exposed part 66 comprises the photosensitive fibre core that is wrapped in by covering.The photosensitive fibre core that exemplifies is made by the compound of silicon dioxide and germanium, but covering can only be made by silicon dioxide.Can improve photosensitivity by adding hydrogen.
Adjustable waveguide fixed mount 70 is located waveguide 50 with respect to overlapping light beam 38 and 40.Different with conventional practice is, light beam 38 and 40 central shaft 46 and 58 intersect each other at 76 places, position of the optical axis 64 that departs from waveguide 50.In other words, the central shaft 46 and 58 corresponding to the peak strength of light beam 38 and 40 is intersecting along the relative displacement position 72 of optical axis 64 and the optical axis 64 of 74 places and waveguide 50.
Relative displacements take place and the comparative result that obtains along optical axis 64 in the peak strength that Fig. 4 and Fig. 5 show space coherent beam 38 and 40.For example, Fig. 4 illustrates peak valley index modulation 78 and keeps required pulse type to change, and mean refractive index 80 is overlapping at light beam 38 and 40 and the scope of interfering in become more constant.Fig. 5 illustrates the finished product Bragg grating and has obtained the desirable zone of reflections 82, and the numerical value of secondary lobe 84 obviously reduces.Steeper side is along 86 and 88 performances of also having improved grating (for example, reduced crosstalk) in the zone of reflections 82.
Preferably the central shaft 46 of two-beam 38 and 40 and 58 is separated half of full duration of its half maximal value intensity at least along optical axis 64.But, for sinc
2Intensity distributions, spacing be approximately half maximal value intensity full duration 0.88 be best.The refractive index that axle 46 and 58 (that is peak strengths) make the grating center along the too little meeting of spacing of optical axis 64 refractive index at its two ends relatively is too big.Spacing too conference makes relative its two ends of refractive index of grating center too small, and can excessively shorten the overlap length between the light beam 38 and 40, and index modulation promptly writes in this overlap length.
Can arrange each parts of interferometer 20 with different modes (increase, reduce or substitute), still obtain the more smooth mean refractive index that is produced by the single-lobe shaped light beam that is positioned at place, partly overlapping fixed position simultaneously.For example, the sinc of light beam 24
2Intensity distributions is the product of particular space light filter 30, but also can use other single-lobe shaped light beam that comprises gaussian beam profile to distribute.If need fully, collimating apparatus 32 can be placed on the back of second spatial light filter 34, perhaps pair of alignment device 32 is placed on the back of beam splitter 36.Can carry out relative orientation with 42,44,52,54 and 56 pairs of light beams 38 of more or less reverberator and 40, and the intersection point 76 of beam axis 46 and 58 can be arranged in the front or the back of the optical axis 64 of waveguide 50.
Can also be used as eyeglass and will be imaged onto on the exposed part 66 of waveguide 50, can amplify or not amplify from the interference figure on an expection plane.Interference figure is contained on described expection plane, otherwise interference figure can be formed directly on the exposed part 66 of waveguide 50.
Fig. 6 shows another embodiment 90 that can obtain similar results.Starting point still is an actinic radiation sources 92, is the excimer laser of 193nm or 248nm such as operation wavelength.Equally, also can use other laser instrument and other wavelength, to adapt to special application or material.Cylindrical lens 96 and combining of spatial light filter 100 have strengthened the spatial coherence of beam of actinic radiation 94.Second spatial light filter 104 receives the light beam 94 of autocollimator 102, further to the intensity distributions shaping of light beam 94.The light beam 94 that catoptron 106 will further be shaped is mapped on another cylindrical lens 108, and these cylindrical lens 108 relative cylindrical lenses 96 have rotated 90 degree, and it is assembled light beam towards the focal line in the axial plane (that is the plane of Fig. 6) of the optical waveguide of making 110.In axial plane, light beam 94 keeps collimation.
Be supported on phase mask 112 on the adjustable fixed mount 114 intercept and capture through collimation/convergent beam 94, and in the axial plane of optical waveguide 110, with light beam 94 be divided into two bundle collimations but the light beam 118 and 120 dispersed relatively.Phase mask 112 itself is a diffraction grating, and it preferably has a constant cycle, and through further arranging, most illumination radiation is mapped on the first order of opposite in sign in the grating.Also can use the combination of other grade, comprise the combination of the zero level and the first order, but the preferably combination of two first order.
Near phase mask 112, two-beam 118 and 120 overlapping and interference.But, be not that phase mask 112 is placed directly on the exposed part 122 of waveguide 110, but with phase mask 112 and exposed part 122 from a distance, make two-beam 118 and 120 peak strength 124 and 126 (they are preferably corresponding to central shaft) along the optical axis 128 of waveguide 110 separately.The spacing of 1mm-5mm is considered to typically, but also can use greater or lesser spacing according to the width and the desirable spectral response of finished product grating of two light beams.
Suppose that (a) optical waveguide 110 is similar to the optical waveguide 50 of Fig. 3; (b) light beam 94 is similar to the light beam 24 of Fig. 3; (c) light beam 118 and 120 angle of diffraction are similar to inclination alpha and the β of Fig. 3; And (d) peak strength 124 and 126 spacings along optical axis 128 are similar to peak strength 72 and 74 spacings along optical axis among Fig. 3 64.So, illustrated as Fig. 4 and Fig. 5, can produce similar grating with the embodiment of Fig. 3 and Fig. 6.Aspect the layout of each parts, also can carry out similar dirigibility.
So far, with regard to two embodiment 3 and 6 single exposure to its relevant waveguide 50 and 110 has been described.Although the improvement of narrating among Fig. 4 and Fig. 5 is substantial, the supplenmentary exposure that is used in particular for regulating the mean refractive index of waveguide cores can bring further improvement, and this kind exposure can not change the variation of index modulation peak valley numerical value.The overlapping light beam of two bundles is preferably adopted in exposure for the second time, but will avoid waveguide cores is produced the interference fringe effect.
Return Fig. 3, can move adjustable waveguide fixed mount 70, to change the peak strength 72 and 74 the spacings of light beam 38 and 40 along optical axis 64 along the direction of arrow 130.For the second time the spacing between exposure period is more preferably greater than the spacing between first time exposure period.The peak valley numerical value change of index modulation has been optimized in exposure for the first time, and the mean refractive index of index modulation has further been optimized in exposure for the second time.In other words, have only exposure for the first time to influence the peak valley numerical value change of index modulation, all influenced the mean refractive index of index modulation but expose for first and second times.
Between second time exposure period,, can prevent to interfere between two light beams by reducing the spatial coherence between the light beam 38 and 40.The spatial light filter 30 that replaces having identical transmission function with amplitude mask can reduce spatial coherence.Can also further reduce spatial coherence with a diffusion eyeglass, perhaps can make light beam 38 and 40 relative shears, to increase its effective spatial deviation.
Another kind method is, by wash out the interference fringe between light beam 38 and 40 along the direction dither optical waveguide of arrow 132.To be exposed to the mean intensity of the interference figure of crossing over a plurality of stripeds along any point of the optical axis 64 of waveguide part 66.
The curve map of Fig. 7 and Fig. 8 shows the further improvement result that the double exposure back obtains.The peak valley numerical value change of index modulation 136 has further been optimized in exposure for the first time, and the planarization in the scope of whole index modulation 136 all has contribution for mean refractive index 138 and expose for first and second times.The spectral response that Fig. 8 draws illustrates secondary lobe 140 and obviously reduces, and has kept the desirable zone of reflections 142 simultaneously.
The embodiment of Fig. 6 is through arranging to obtain analogous result.For example, phase mask 112 can relatively move on adjustable fixed mount 114 along the direction of arrow 146, to change the peak strength 124 and 126 spacings along optical axis 128 of light beam 118 and 120.Also can be similar to the embodiment of Fig. 3, change the spacing of peak strength by the waveguide on the moveable support 148 110.Equally, by waveguide 110 of direction dither or phase mask 112, can reduce spatial coherence or wash out striped, thereby avoid interference effect along arrow 150.
Although double exposure is called for the first time and exposure for the second time other with vision area, double exposure can be by the order of first back second earlier, also can be by the order of second back first earlier.Although have at least once peak strength 72,74 or 124,126 optical axises 64 or 128 that displacement has taken place in the double exposure along optical waveguide 50 or 110, but according to required Sidelobe Suppression requirement, the peak strength of one other exposure needn't be subjected to displacement along optical axis 64 or 128 in the double exposure.
The index modulation spacing of the index modulation gap ratio Bragg grating of long-period gratings is much bigger, and aspect inscription more selection can be arranged, and comprises the digital amplitude mask.But, being exposed to the light beam of two bundle relative displacements simultaneously in order to make grating, exposure is for the second time especially used the exposure of phase mask to wash out striped simultaneously by the mean refractive index planarization that makes longer index modulation to improve performance.
Particularly useful in communication system according to the Bragg grating that the present invention makes.For example, Bragg grating can be used to add or deduct special channel, perhaps spends individually segregated channel of multiplexed ability.Other application comprises sensor, dispersion compensator, perhaps the laser pumping stabilizator.Play preferably according to the long-period gratings of manufacturing of the present invention that spectrum is selected or band removes reinstating of light filter, be used to improve working condition such as devices such as image intensifer and denoisers.
Claims (60)
1. light filter that in optical medium, forms, it is characterized in that, described light filter has the index modulation of a series of intensity pattern corresponding to the actinic radiation interfering beam along optical axis, and the axle of described interfering beam is in different fixed positions along the optical axis relative displacement.
2. light filter as claimed in claim 1, it is characterized in that, described index modulation is numerically corresponding to the relative intensity of interference figure between the described interfering beam, the average fringe contrast of described interference figure changes along optical axis, and this changes greater than intensity pattern mean value along the variation of optical axis with a part.
3. light filter as claimed in claim 2 is characterized in that described interfering beam is a certain amount of along the optical axis relative displacement, causes the mean value of intensity pattern to remain unchanged substantially in described interfering beam overlapping areas.
4. light filter as claimed in claim 1 is characterized in that, the described axle of interfering beam and optical axis intersection, and intersection location is half of full duration of half maximal value intensity at least separately.
5. light filter as claimed in claim 4 is characterized in that, the described axle of interfering beam and optical axis intersection, intersection location at least separately half maximal value intensity full duration about 0.88.
6. light filter as claimed in claim 5 is characterized in that described interfering beam has sinc
2Strength distribution curve.
7. light filter as claimed in claim 1 is characterized in that, the described axle of interfering beam intersects in the optical axis front of optical medium.
8. light filter as claimed in claim 1 is characterized in that, the described axle of interfering beam intersects in the optical axis back of optical medium.
9. a system that is used for making at the optical waveguide medium light filter is characterized in that, comprising:
Spatial light filter is used to increase the spatial coherence of the light beam that actinic radiation sources penetrates;
Phase mask is used for converting space coherent beam to two beam interferometer light beams, at light beam increased space coherence internal radiation optical waveguide medium, thereby produces index modulation in medium; And
Described phase mask leaves optical waveguide medium one segment distance, this distance make interfering beam peak strength along the optical waveguide medium separately, and the combined strength that makes interfering beam at interfering beam along planarization in the overlapping scope of optical waveguide medium.
10. system as claimed in claim 9 is characterized in that, the described peak strength of light beam is along optical waveguide medium half of full duration of light beam half maximal value intensity at least separately.
11. system as claimed in claim 9 is characterized in that, described spatial light filter is given space coherent beam with sinc
2Intensity distributions.
12. system as claimed in claim 11 is characterized in that, the described axle of interfering beam and optical axis intersection, intersection location at least separately half maximal value intensity full duration about 0.88.
13. system as claimed in claim 9 is characterized in that, also comprises a governor motion, is used to change the spacing between phase mask and the optical waveguide medium, thereby the control peak strength is along the spacing of optical waveguide medium.
14. system as claimed in claim 13, it is characterized in that, described phase mask and optical waveguide medium separate second distance, the peak strength that this distance makes overlapping light beam is along optical waveguide medium one section different distance separately, and causes that the variation of mean refractive index in the overlapping scope of interfering beam diminishes in the optical waveguide medium.
15. system as claimed in claim 14 is characterized in that, also comprises following apparatus, produces the striped effect relevant with overlapping light beam when this device is used to avoid being in described second distance between phase mask and optical waveguide medium.
16. system as claimed in claim 15 is characterized in that, is used to avoid the described device of striped effect to make the overlapping relatively light beam of optical waveguide medium make dither.
17. system as claimed in claim 15 is characterized in that, is used to avoid the described device of striped effect to make phase mask make dither with respect to space coherent beam.
18. system as claimed in claim 15 is characterized in that, is used to avoid the described device of striped effect to reduce the spatial coherence of two beam interferometer light.
19. system as claimed in claim 9 is characterized in that, described phase mask has constant spacing.
20. a method that forms light filter is characterized in that, may further comprise the steps:
One optical waveguide medium is provided, and its refractive index can change through the actinic radiation exposure;
With the beam of actinic radiation orientation of two bundle inclinations, so that the irradiates light waveguide medium; And
In the spatial coherence scope of two light beams, to optical waveguide medium location, away from intersection point one segment distance of two diagonal beam, so that form an interference figure along the optical waveguide medium, the mean intensity of this interference figure changes less.
21. method as claimed in claim 20 is characterized in that, described positioning step comprises that the peak strength that makes two diagonal beam is along optical waveguide medium half of full duration of light beam half maximal value intensity at least separately.
22. method as claimed in claim 20 is characterized in that, also comprises a public beam of actinic radiation is divided into two bundle diagonal beam.
23. method as claimed in claim 22 is characterized in that, also comprises the step of public beam of actinic radiation being carried out spatial filtering.
24. method as claimed in claim 23 is characterized in that, also comprises public light beam is arranged to having sinc
2The step of intensity distributions.
25. method as claimed in claim 22 is characterized in that, carries out the step of the public light beam of described separation with beam splitter.
26. method as claimed in claim 22 is characterized in that, carries out the step of the public light beam of described separation with phase mask.
27. method as claimed in claim 20, it is characterized in that, further comprising the steps of, be about to optical waveguide medium location, away from one section different distance of intersection point of two bundle diagonal beam, thereby further reduce in the interference figure spatial dimension, to give the variation of the mean intensity of optical waveguide medium.
28. a method of making light filter in the optical waveguide medium is characterized in that, comprising:
With first group of overlapping beam of actinic radiation irradiates light waveguide medium, the peak strength of first group of light beam is positioned at along first fixedly on the relative position of optical waveguide medium;
Produce index modulation in the optical waveguide medium, described modulation is corresponding to by the locational first group of interference figure that overlapping light beam forms on the optical waveguide medium of first stationary phase;
With second group of overlapping beam of actinic radiation irradiates light waveguide medium, the peak strength of first group of light beam is positioned at along second fixedly on the relative position of optical waveguide medium; And
With the second fixing mean refractive index of second group of irradiated optical waveguide medium of overlapping light beam regulation on the relative position, present less variation in the whole index modulation scope that makes the mean refractive index of illuminated optical waveguide medium in the optical waveguide medium, form.
29. method as claimed in claim 28 is characterized in that, described regulating step comprises the steps, promptly makes mean refractive index constant substantially in whole index modulation scope.
30. method as claimed in claim 28, it is characterized in that, comprise the steps: promptly to make the peak strength of overlapping light beam along optical waveguide medium half of full duration of light beam half maximal value intensity at least separately with the described step of second group of overlapping light beam irradiates optical waveguide medium.
31. method as claimed in claim 28 is characterized in that, also comprises the steps, promptly a public light beam is carried out spatial filtering, and described first group of overlapping light beam comes out from described public beam separation.
32. method as claimed in claim 28 is characterized in that, also comprises the steps: promptly to stop second group of overlapping light beam that index modulation is changed along the optical waveguide medium.
33. a light filter of making according to the described method of claim 28 is characterized in that described light filter has a photosensitive waveguide medium.
34. a method of making light filter is characterized in that, may further comprise the steps:
One optical waveguide medium is provided, and its refractive index can change by the actinic radiation exposure;
The first bundle beam of actinic radiation was penetrated a phase mask, and described phase mask is positioned at the primary importance of relative optical waveguide;
First beam diffraction is become first group of overlapping light beam, produce index modulation in order to optical axis along the optical waveguide medium;
With respect to optical waveguide, phase mask is moved to the second place from primary importance;
The second bundle beam of actinic radiation was penetrated the phase mask that is positioned at the second place; And
Second beam diffraction is become second group of overlapping light beam, change mean refractive index in order to optical axis along the optical waveguide medium.
35. method as claimed in claim 34 is characterized in that, described mobile step comprises, phase mask is moved along the vertical direction of the optical axis of optical waveguide substantially.
36. method as claimed in claim 35 is characterized in that, two groups of overlapping light beams all are positioned on the coaxial plane of optical waveguide.
37. method as claimed in claim 35 is characterized in that, the second place makes phase mask and optical waveguide at least at a distance of a millimeter.
38. method as claimed in claim 34 is characterized in that, phase mask has a constant spacing.
39. method as claimed in claim 34 is characterized in that, the peak strength of second group of overlapping light beam is along optical waveguide medium half of full duration of light beam half maximal value intensity at least separately.
40. method as claimed in claim 34 is characterized in that, the step that is used for diffraction second light beam comprises the steps: promptly to make that mean refractive index optical axis along the optical waveguide medium in the overlapping scope of first group of overlapping light beam is constant substantially.
41. method as claimed in claim 34 is characterized in that, also comprises the steps, promptly the first bundle beam of actinic radiation is carried out spatial filtering, to improve spatial coherence.
42. method as claimed in claim 34 is characterized in that, and is further comprising the steps of, promptly stops second group of overlapping light beam that index modulation is changed along optical axis.
43. a light filter of making according to the described method of claim 34 is characterized in that described light filter has a photosensitive waveguide medium.
44. light filter as claimed in claim 43 is characterized in that, described light filter is a Bragg grating.
45. light filter as claimed in claim 43 is characterized in that, described light filter is a long-period gratings.
46. a light filter apodization, wherein said light filter forms by carrying out index modulation along the waveguide medium optical axis, it is characterized in that, said method comprising the steps of:
A branch of beam of actinic radiation is divided into overlapping light beam, and the axle of described overlapping light beam extends along its direction of propagation;
With overlapping light beam irradiates waveguide medium;
An optical axis along waveguide medium of overlapping light beam is separated; And
Prevention changes along optical axis because of the interference effect between the overlapping light beam causes index modulation, so that can regulate mean refractive index along optical axis, makes the index modulation value constant substantially along optical axis.
47. method as claimed in claim 46 is characterized in that, described division step comprises the steps, the axle that is about to overlapping light beam is along the optical axis of waveguide medium half of full duration of light beam half maximal value intensity at least separately.
48. method as claimed in claim 46 is characterized in that, described prevention step comprises the step that makes waveguide medium make dither with respect to overlapping light beam.
49. method as claimed in claim 46 is characterized in that, described separating step comprises the step with the phase mask separating light beam.
50. method as claimed in claim 49 is characterized in that, described prevention step provides the step of dither phase mask.
51. method as claimed in claim 46 is characterized in that, described prevention step comprises the step that reduces overlapping light beam spatial coherence.
52. cut the light filter that toe obtains according to the described method of claim 46 for one kind, it is characterized in that described light filter has a photosensitive waveguide medium.
53. light filter as claimed in claim 52 is characterized in that, described light filter is a Bragg grating.
54. light filter as claimed in claim 52 is characterized in that, described light filter is a long-period gratings.
55. a light filter apodization, wherein said light filter forms by carrying out index modulation along the waveguide medium optical axis, it is characterized in that, said method comprising the steps of:
A branch of beam of actinic radiation was penetrated a phase mask, and described phase mask is divided into overlapping light beam with this light beam, is radiated on the waveguide medium;
Make phase mask leave waveguide medium one segment distance, in order to separate the peak strength of overlapping light beam along optical axis; And
Prevention changes along optical axis because of the interference effect between the overlapping light beam causes index modulation, so that can regulate mean refractive index along optical axis, makes the index modulation value constant substantially along optical axis.
56. method as claimed in claim 55 is characterized in that, described division step may further comprise the steps, even the peak strength of overlapping light beam is along optical axis half of full duration of light beam half maximal value intensity at least separately.
57. method as claimed in claim 55 is characterized in that, described prevention step provides the step that makes the phase mask dither.
58. method as claimed in claim 55 is characterized in that, described prevention step provides the step that makes the overlapping relatively light beam of waveguide medium make dither.
59. method as claimed in claim 55 is characterized in that, described prevention step comprises the step that reduces overlapping light beam spatial coherence.
60. cut the light filter that toe obtains according to the described method of claim 55 for one kind, it is characterized in that described light filter has a photosensitive waveguide medium.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US9154798P | 1998-07-01 | 1998-07-01 | |
| US60/091,547 | 1998-07-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN1342269A true CN1342269A (en) | 2002-03-27 |
Family
ID=22228342
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN99810053A Pending CN1342269A (en) | 1998-07-01 | 1999-06-30 | Apodization of optical filters formed in photosensitive media |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP1092165A4 (en) |
| JP (1) | JP2002519742A (en) |
| KR (1) | KR20010053247A (en) |
| CN (1) | CN1342269A (en) |
| AU (1) | AU4852399A (en) |
| CA (1) | CA2336329A1 (en) |
| WO (1) | WO2000002068A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102590951A (en) * | 2012-02-29 | 2012-07-18 | 浙江工业大学 | Photorefractive long-period waveguide grating filter and manufacturing method thereof |
| CN102662218A (en) * | 2012-05-31 | 2012-09-12 | 东南大学 | Wrinkle type apodization waveguide Bragg grating filter and manufacturing method thereof |
| CN102707584A (en) * | 2012-06-15 | 2012-10-03 | 杭州士兰明芯科技有限公司 | Double-light-beam exposure system and method for manufacturing photonic crystal mask layer |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6553163B2 (en) | 2000-03-30 | 2003-04-22 | Corning, Incorporated | Method and apparatus for writing a Bragg grating in a waveguide |
| EP1139123A1 (en) * | 2000-03-30 | 2001-10-04 | Optical Technologies Italia S.p.A. | Method and apparatus for writing a Bragg grating in a waveguide |
| WO2001088573A1 (en) * | 2000-05-18 | 2001-11-22 | Sumitomo Electric Industries, Ltd. | Optical waveguide type diffraction grating and method for manufacturing the same |
| EP1207410A1 (en) * | 2000-11-16 | 2002-05-22 | Corning O.T.I. S.p.A. | Method and equipment for writing a bragg grating in a waveguide |
| US6591039B2 (en) * | 2000-11-16 | 2003-07-08 | Corning Oil Spa | Method and equipment for writing a Bragg grating in a waveguide |
| CA2354321A1 (en) | 2001-07-26 | 2003-01-26 | Viamode Photonics Inc. | Apparatus for writing features in or on photosensitive medium |
| US7280206B2 (en) * | 2004-09-13 | 2007-10-09 | Agilent Technologies, Inc. | Method and apparatus to improve the dynamic range of optical devices using spatial apodization |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5367588A (en) * | 1992-10-29 | 1994-11-22 | Her Majesty The Queen In Right Of Canada, As Represented By The Minister Of Communications | Method of fabricating Bragg gratings using a silica glass phase grating mask and mask used by same |
| US5363239A (en) * | 1992-12-23 | 1994-11-08 | At&T Bell Laboratories | Method for forming spatially-varying distributed Bragg reflectors in optical media |
| GB2289771B (en) * | 1994-05-26 | 1997-07-30 | Northern Telecom Ltd | Forming Bragg gratings in photosensitive waveguides |
| FR2728356B1 (en) * | 1994-12-15 | 1997-01-31 | Alcatel Fibres Optiques | DEVICE FOR PRINTING A BRAGG NETWORK IN AN OPTICAL FIBER |
| JP2000501852A (en) * | 1995-12-12 | 2000-02-15 | ブリティッシュ・テレコミュニケーションズ・パブリック・リミテッド・カンパニー | Method of forming refractive index grating |
| US5848207A (en) * | 1996-08-29 | 1998-12-08 | Hitachi Cable, Ltd. | Optical device formed with grating therein, add/drop filter using same, and method of fabricating same |
| CA2202308C (en) * | 1996-04-19 | 2001-05-08 | Michihiro Nakai | Optical waveguide grating and production method therefor |
| AUPO512697A0 (en) * | 1997-02-14 | 1997-04-11 | Indx Pty Ltd | Improvements in a system for writing gratings |
-
1999
- 1999-06-30 WO PCT/US1999/014942 patent/WO2000002068A1/en not_active Application Discontinuation
- 1999-06-30 KR KR1020007014919A patent/KR20010053247A/en not_active Application Discontinuation
- 1999-06-30 CA CA002336329A patent/CA2336329A1/en not_active Abandoned
- 1999-06-30 AU AU48523/99A patent/AU4852399A/en not_active Abandoned
- 1999-06-30 EP EP99932157A patent/EP1092165A4/en not_active Withdrawn
- 1999-06-30 JP JP2000558408A patent/JP2002519742A/en not_active Withdrawn
- 1999-06-30 CN CN99810053A patent/CN1342269A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102590951A (en) * | 2012-02-29 | 2012-07-18 | 浙江工业大学 | Photorefractive long-period waveguide grating filter and manufacturing method thereof |
| CN102662218A (en) * | 2012-05-31 | 2012-09-12 | 东南大学 | Wrinkle type apodization waveguide Bragg grating filter and manufacturing method thereof |
| CN102707584A (en) * | 2012-06-15 | 2012-10-03 | 杭州士兰明芯科技有限公司 | Double-light-beam exposure system and method for manufacturing photonic crystal mask layer |
| CN102707584B (en) * | 2012-06-15 | 2014-03-12 | 杭州士兰明芯科技有限公司 | Double-light-beam exposure system and method for manufacturing photonic crystal mask layer |
Also Published As
| Publication number | Publication date |
|---|---|
| WO2000002068A1 (en) | 2000-01-13 |
| EP1092165A4 (en) | 2005-06-22 |
| KR20010053247A (en) | 2001-06-25 |
| AU4852399A (en) | 2000-01-24 |
| EP1092165A1 (en) | 2001-04-18 |
| JP2002519742A (en) | 2002-07-02 |
| CA2336329A1 (en) | 2000-01-13 |
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